Non-linear resistance element

ABSTRACT

A varistor whose ceramic body contains bismuth oxide and antimony oxide containing semiconducting titanium oxide having a relatively low C-value and a low Beta value.

United States Patent 1 l Yperman et al. 1 Feb. 6, 1973 [541 NON -LINEAR RESISTANCE ELEMENT M 58 Field of Search "ass/20 25; '[75] Inventors: Jean Michel Baudry Ghislain Yper'- 313/238; 252/520 man Woluwe; Jean Rodolphe I Rapaiille, Brussels, both of Belgium [56] References cued [73] Assignee: U.S. Philips Corporation, New UNITED STATES PATENTS 9 I 2,885,521 5 1959 Fotland I .,..33s/20 x Filed: 7 Feb. 19, 7 31,299,332 1/1967 Seburi "Y. ..317/238 X [2 1-] Appl. No.: 116,922 9 j Primary Examiner-D. F. Duggan v Attorney-Frank R. Trifari [30] Foreign Application Priority Data [57] v ABSTRACT v I 1970 Netherlands "7003118 A varistor whose ceramic body contains bismuth oxide I I I and antimony oxide containing semiconducting titani- ..338/20, 252/520 um oxide having a relatively low Cwalue and a low B value.

2 Claims, 1 Drawing Figure INVENTORS I v JEAN M. YPERMAN BYJEAN OLPE RAPAJLL E The invention relates to a non-linear resistance element having a large voltage dependence of the resistance and in which the resistance body comprises sintered ceramic ferroelectric material. Such nonlinear resistance elements are sometimes referred to as varistors.

For such a resistance element the relation between current intensity and voltage may be defined by the formula:

- in this formula V represents the voltage across the resistor in Volts, 1 represents the current through the resistor in amperes, C represents the voltage across the resistor at I= 1 amp. and B represents a number smaller than 1.

Known varistors are manufactured by sintering fine particles of silicon carbide and a ceramic binder and/or a conducting material, for example, graphite. Varistors thus manufactured with a conducting binder have a comparatively small electric resistance, that is to say, a relatively small value for C and a relatively large value for B. Varistors manufactured from silicon carbide and a non-conducting binder have a comparatively large electric resistance, that is to say, a relatively large value for C and a relatively small value for B. In both cases the value of B lie between 0.15 and 0.30 in practice.

In known silicon carbide varistors, the value of B is often dependent on V; at comparatively low values of V, B is larger than at comparatively high values of V. This has drawbacks for certain applications inter alia, for voltage stabilization, rendering small motor free from interference (limitation of the over-voltage) and protection of collectors in small motors (tape recorders, record players).

Theobject of the present invention is to provide a varistor in which the value of B is not dependentor is only dependent to aslight extenton the value of V. A further object of the invention is to provide a varistor whose values of B are small also at low values of C. Such a varistor is particularly suitable for the said applications.

The invention relates to a non-linear resistance element whose ceramic resistance body provided with electrodes is a ceramic body mainly consisting of semiconducting titanium oxide and is characterized in that the ceramic body contains per mol of titanium oxide, 0005-01 and preferably 0.03-0.05 mol of bismuth oxide and 0.00l-0.05 and preferably0.004-0.0l mol of antimony oxide.

Resistance bodies for non-linear resistance elements according to the inventionmay be manufactured, for example, in the following manner. A mixture of TiO Bip and sb,o,, or. of compounds which change into I these oxides upon heating, is homogeneized by wet ample 20 percent of chromium, on the surfaces of the body on which the electrodes are to be provided and subsequently by vapor depositing likewise in vacuo on this layer a layer of solderable metal, for example, silver.

A more detailed description of the manufacture of a resistance element according to the invention will be described hereinafter by way of example.

79.9 g (1 mol) TiO 19.8 g (0.04 mol) Bi O and 1.45 g (0.0005 mol) Sb 0 were introduced in a porcelain ball mill with 350 mls of ethanol and mixed and ground for 15 hours. Subsequently the mixture was dried in a furnace at 50C. The dried mixture was then mixed with 40 mls of a mixture obtained by mixing 45 g of polyvinyl acetate 1,000 mls of methylethylketone and 10 mls of dibutylphthalate. Subsequently cylindrical bodies (thickness 1.0 mm, diameter 5.6 mm) were moulded from the mass obtained. These bodies were introduced into a furnace and heated in air at 1,490C for 5 minutes. After cooling the end-faces of the cylindrical bodies were provided with electrodes in the known manner mentioned above.

The electrical properties of the varistor thus manufactured and those of varistors manufactured in a similar manner whose compositions of the ceramic re sistance bodies are different are shown in the table together with these compositions.

It was found that varistors according to the invention can be improved in some respects (lowB -values), by incorporating lead oxide (Pb0 or PbO) or an oxide of barium, strontium or calcium in the ceramic resistance body up to a quantity of 0.1 mol of these oxides per 1 mol of titanium oxide (TiO Resistance bodies according to the invention containing PbO BaO, SrO or CaO may be manufactured in accordance with the above-mentioned method. The desired quantity of one or more of these oxides or of compounds which change into these oxides upon heating are added to the starting mixture containing TiO Bi O and Sb,0

The following table shows data of different Examples of non-linear resistance elements according to the invention. The columns 1, 2, 3, and 4 state the quantities of oxides contained in the resistance body in addition to Tio The quantities of these oxides are stated in mol per mol of Ti0 The resistance body according to Example I, thus contains 0.005 mol of Sb O and 0.05 mol of 131 0, per mol of TiO,. Columns 5 and 6 show the sintering temperature (in C) and sintering period (in minutes), respectively. Columns 7 and 8 show the voltage V (in Volts) at which a current of 1 mA is reached and the associated value of B respectively. Column 9 shows the numbers of the examples.

sintering sintering SbzQ- B1203 BaO PbOg temp. period V 5 ment consists of a cylindrical ceramic resistance body 1 7 whose end-faces 2 and 3 are provided with electrodes 4 and 5 by vapor depositing in vacuo successively a layer of chrome-nickel alloy and a layer of silver. Supply wires 8 and 9 are provided by means of solder 6 and 7.

What is claimed is:

l. A non-linear resistance element whose ceramic resistance body provided with electrodes is a ceramic body mainly consisting of semiconducting titanium oxide, wherein the ceramic body contains per mol of titanium oxide 0.005-0.1 mol of bismuth oxide and 0.0010.05 mol of antimony oxide.

2. A non-linear resistance element as claimed in claim 1, wherein the ceramic body contains per mol of titanium oxide 0.03-0.05 mol of bismuth oxide and 0004-00] mol of antimony oxide. 

1. A non-linear resistance element whose ceramic resistance body provided with electrodes is a ceramIc body mainly consisting of semiconducting titanium oxide, wherein the ceramic body contains per mol of titanium oxide 0.005-0.1 mol of bismuth oxide and 0.001-0.05 mol of antimony oxide. 